LCD devices are used as displays on a variety of electronic products, such as computer monitors and motor vehicle cruise control panels. Existing LCD types include, for example, the twisted nematic liquid crystal display (TN-LCD) and the in-plane switching liquid crystal display (IPS-LCD). The TN-LCD often has the problem of a narrow viewing angle, and so the IPS-LCD was developed to overcome this disadvantage. The IPS-LCD typically has one or more common electrodes and a plurality of pixel electrodes all disposed on one of two parallel substrates. Liquid crystal molecules are interposed between the substrates. The electrodes drive the liquid crystal molecules with an electric field. The resulting electric field is substantially in a plane parallel to the substrates. Such a configuration provides a wide viewing angle.
However, the common electrodes and pixel electrodes are formed of opaque metals, giving the IPS-LCD a low aperture ratio and low transmittance. Thus, a fringe field switching liquid crystal display (FFS-LCD) with a flat plate-like common electrode has been developed in order to improve on the aperture ratio and transmittance. The FFS-LCD is characterized by its driving electric field, which is between each pixel electrode and the common electrode. Because the common electrode is transparent, the FFS-LCD can typically attain a higher aperture ratio and a higher transmittance.
FIG. 7 is a schematic, side cross-sectional view of part of a typical FFS-LCD device. The FFS-LCD device 1 includes a first substrate 11 and a second substrate 12, with the first and second substrates 11, 12 being spaced apart a predetermined distance. A liquid crystal layer 10 having a multiplicity of liquid crystal molecules (not labeled) is disposed between the first and second substrates 11, 12. A backlight module (not shown) is disposed under the second substrate 12 for providing illumination.
A color filter 13 and a first alignment film 14 are formed on an inner surface of the first substrate 11, in that order from top to bottom. A common electrode 15 and a plurality of pixel electrodes 18 are disposed at an inner surface of the second substrate 12, with an insulating layer 16 interposed between the common electrode 15 and the pixel electrodes 18. A second alignment film 17 is formed on the insulating layer 16, such that the second alignment film 17 also covers the pixel electrodes 18.
Also referring to FIG. 8, this is a top plan view of part of the second substrate 12. Two gate lines 121 and two data lines 122 define a pixel region of the FFS-LCD device 1. The data lines 122 are parallel to but spaced apart from each other, and are substantially perpendicular to the gate lines 121. A thin film transistor (TFT) 120 used as a switching element is arranged at the intersection of one gate line 121 and the corresponding data line 122.
The pixel and common electrodes 18, 15 are formed in the pixel region. The pixel and common electrodes 18, 15 are made of a transparent conductive material such as indium-tin-oxide (ITO) or indium-zinc-oxide (IZO). The pixel electrode 18 is electrically connected to the source electrode of the TFT 120, in order to obtain displaying signals therefrom. The common electrode 15 is electrically connected to common line (not labeled), in order to obtain common voltage signals therefrom.
The pixel electrode 18 includes a plurality of straight comb tooth portions (not labeled), which all extend in a same direction and are substantially parallel to each other. When the FFS-LCD device 1 is driven, a strong fringe electric field is formed between the common electrode 15 and the pixel electrode 18. The liquid crystal molecules disposed over the common electrode 15 and pixel electrodes 18 are driven by this electric field to have a corresponding orientation. The liquid crystal molecules are rotated only in a single direction; that is, the FFS-LCD device 1 has a single domain. Consequently, the FFS-LCD device 1 has a high aperture ratio and high transmittance; but the FFS-LCD device 1 also exhibits color shift when it is obliquely viewed in different directions.
Referring to FIG. 9, this is a schematic, top plan view of a pixel region of another typical FFS-LCD device. The FFS-LCD device 2 has a structure similar to that of the FFS-LCD device 1. However, a pixel electrode 250 has a plurality of slits 260 therein. The slits 260 are divided into a first set of slits 261 and a second set of slits 262. The first set of slits 261 are parallel to each other and oriented in a first direction. The second set of the slits 262 are parallel to each other and oriented in a second direction. Thus, at the center of the pixel electrode 250, the first set and second sets of slits 261, 262 cross and form some “V”-shaped (or “Y”-shaped) elbows thereat. When a voltage is applied between the pixel and common electrodes 250, 280, a horizontal in-plane electric field in two directions is established between the pixel and common electrodes 250, 280. Thus, the liquid crystal display device 2 has two domains so as to reduce color shift.
However, at each “V”-shaped elbow portion, an electric field generated by voltage is abnormal, and liquid crystal molecules thereat are oriented disorderly. Further, disinclination of the liquid crystal molecules occurs at the elbow portion, and this decreases the transmittance and display quality of the LCD device 2.
Accordingly, what is needed is an FFS-LCD device that can overcome the above-described deficiencies.